linux-kernel - Re: [PATCH 2/2] xen-pciback: prepare for the split for stub and PV

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Date:   Thu, 23 Sep 2021 11:05:03 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Oleksandr Andrushchenko <Oleksandr_Andrushchenko@...m.com>,
        Stefano Stabellini <sstabellini@...nel.org>
Cc:     "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "boris.ostrovsky@...cle.com" <boris.ostrovsky@...cle.com>,
        "julien@....org" <julien@....org>,
        "jbeulich@...e.com" <jbeulich@...e.com>,
        Oleksandr Andrushchenko <andr2000@...il.com>
Subject: Re: [PATCH 2/2] xen-pciback: prepare for the split for stub and PV

On 23.09.21 11:02, Oleksandr Andrushchenko wrote:
> 
> On 23.09.21 00:10, Stefano Stabellini wrote:
>> On Wed, 22 Sep 2021, Oleksandr Andrushchenko wrote:
>>> --- a/drivers/xen/xen-pciback/xenbus.c
>>> +++ b/drivers/xen/xen-pciback/xenbus.c
>>> @@ -743,6 +743,9 @@ const struct xen_pcibk_backend *__read_mostly xen_pcibk_backend;
>>>    
>>>    int __init xen_pcibk_xenbus_register(void)
>>>    {
>>> +	if (!xen_pcibk_pv_support())
>>> +		return 0;
>> Is this truly enough to stop the PV backend from initializing? Have you
>> actually tested it to make sure? If it works, amazing! I am quite happy
>> about this approach :-)
> 
> Well, I put some logs into the driver and saw nothing obvious pointing
> 
> to any backend activities (probably this is also because I don't have any
> 
> frontend). I see that the xenbus driver is not registered. In XenStore I see:
> 
> root@...0:~# xenstore-ls -f | grep pci
> /local/domain/0/backend/pci = ""
> /local/domain/0/backend/pci/2 = ""
> /local/domain/0/backend/pci/2/0 = ""
> /local/domain/0/backend/pci/2/0/frontend = "/local/domain/2/device/pci/0"
> /local/domain/0/backend/pci/2/0/frontend-id = "2"
> /local/domain/0/backend/pci/2/0/online = "1"
> /local/domain/0/backend/pci/2/0/state = "1"
> /local/domain/0/backend/pci/2/0/domain = "DomU"
> /local/domain/0/backend/pci/2/0/key-0 = "0000:03:00.0"
> /local/domain/0/backend/pci/2/0/dev-0 = "0000:03:00.0"
> /local/domain/0/backend/pci/2/0/opts-0 = "msitranslate=0,power_mgmt=0,permissive=0,rdm_policy=strict"
> /local/domain/0/backend/pci/2/0/state-0 = "1"
> /local/domain/0/backend/pci/2/0/num_devs = "1"
> /local/domain/2/device/pci = ""
> /local/domain/2/device/pci/0 = ""
> /local/domain/2/device/pci/0/backend = "/local/domain/0/backend/pci/2/0"
> /local/domain/2/device/pci/0/backend-id = "0"
> /local/domain/2/device/pci/0/state = "1"
> /libxl/pci = ""
> /libxl/pci/0000-03-00-0 = ""
> /libxl/pci/0000-03-00-0/domid = "2"
> 
> But IIUIC these come from the toolstack
> 
> @Juergen, do you know how to check if the backend is indeed not running
> 
> or the above should be enough to prove?

I don't see how the backend could be running without being registered
with xenbus. It won't receive any watches, so there is no way a
connection with a frontend could be established.


Juergen


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